How many plasma exchanges to cure thrombotic thrombocytopenic purpura?

7 patients were treated by plasma exchanges and antiplatelet drugs for thrombotic thrombocytopenic purpura (TTP). The effectiveness of therapy was reviewed daily and retrospectively estimated on day 3, d6, d9, and d12. 6 of these 7 patients were cured. The low predictive value of the initial response to therapy is underlined. The clinical and biological status on d12 seems to have the best predictive value for the final outcome. These data encourage us to continue the plasma exchanges until d12, whatever the initial response to therapy in TTP.